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JenkinsApplication

CVE-2021-21691

CRITICAL · 9.8 CVSS v3.1 Published 2021-11-04
Fix available
A fix is available. Upgrade to 2.303.3 / 2.319 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Creating symbolic links is possible without the 'symlink' agent-to-controller access control permission in Jenkins 2.318 and earlier, LTS 2.303.2 and earlier.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Jenkins agents can create symbolic links on the controller node without possessing the required 'symlink' agent-to-controller access control permission, effectively bypassing the intended permission model in Jenkins 2.318 and earlier, LTS 2.303.2 and earlier.

MitigationUpgrade Jenkins to version 2.319 or later (or LTS 2.303.3 or later) to obtain the patched version that properly enforces the symlink permission requirement.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
JenkinsApplication
Affected:< 2.303.3< 2.319

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check installed Jenkins version
    Access the Jenkins web UI: go to Manage Jenkins > About Jenkins, or run `java -jar jenkins.war --version` from the command line if you have direct access
    Affected if The version is earlier than 2.303.3 for LTS or earlier than 2.319 for weekly releases
  2. Verify agent connectivity is enabled
    Go to Manage Jenkins > Manage Nodes. Check if any agents (permanent or cloud) are configured and connected to the controller
    Affected if Agents are configured and connected to the controller; the vulnerability only applies when agent-to-controller communication is active
  3. Inspect agent-to-controller access control for symlink permission
    Go to Manage Jenkins > Configure Global Security. Locate the 'Agent - Agent' or 'Agent-to-controller access control' section. Check if 'symlink' permission is listed and required for agents
    Affected if The symlink permission is not explicitly enforced or is missing from the agent permission set
  4. Audit controller filesystem for unexpected symlinks
    Review the Jenkins home directory and related controller paths for symbolic links that may have been created by agents without proper authorization
    Affected if Unexpected symbolic links exist in Jenkins directories that were not created by administrator action

You are affected if your Jenkins version is below 2.303.3 (LTS) or below 2.319 (weekly) AND you have active agents configured, because the vulnerability allows agents to bypass symlink permission checks.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 2.303.3 / 2.319 or later
Fixed in 2.303.32.319
Interim mitigation

Upgrade Jenkins to version 2.319 or later (or LTS 2.303.3 or later) to obtain the patched version that properly enforces the symlink permission requirement.

Recommended fix High confidence

Jenkins 2.319 (weekly) or Jenkins LTS 2.303.3 (LTS)

  1. 1. Back up your Jenkins home directory and configuration before upgrading.
  2. 2. Download Jenkins 2.319 (weekly release) or Jenkins LTS 2.303.3 (long-term support release) from the official Jenkins downloads page (https://www.jenkins.io/download/).
  3. 3. Stop the Jenkins service.
  4. 4. Replace the Jenkins WAR file (jenkins.war) with the new version from step 2.
  5. 5. Start the Jenkins service.
  6. 6. Verify the upgrade by checking the Jenkins version in Manage Jenkins > About Jenkins.
  7. 7. Confirm the 'symlink' agent-to-controller access control permission is now properly enforced.
Caveat Review plugin compatibility before upgrading, as some plugins may require updates for the new Jenkins version.

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Jenkins Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing6.0 h
  • Review / QA2.0 h
14.0 hours of engineering $2,380
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,808.

Scan for this in your stack

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-21691 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data